By Kim Bo-eunMultiple reports of ships allegedly carrying North Korean coal to South Korea are expected to weigh on the alliance between South Korea and the U.S., despite the two governments stating that this is an excessive concern. But these discoveries are becoming a sensitive issue for the U.S., which has vowed to maintain sanctions strictly until the North takes concrete denuclearization steps.The government is currently investigating nine instances of suspected North Korean coal imports. The United Nations Security Council (UNSC) sanctions imposed last August ban Pyongyang from exporting coal, iron and other mineral resources, and member states from buying them. A further damning allegation is that suspected North Korean coal was bought by a subsidiary of the state-run Korea Electric Power Corporation (KEPCO).The U.S. has maintained a clear stance on North Korean sanctions, with Washington issuing an enforcement advisory last month, days after Secretary of State Mike Pompeo visited the UNSC and called for the strict maintenance of the restrictions imposed on Pyongyang."We still want strict enforcement of all the sanctions _ we continuously speak with all the countries in the region about the importance of that," National Security Adviser John Bolton said in an interview with Fox News, referring to the cases under investigation."We're not going to tolerate diminution of the effect of the sanctions and will take necessary steps including enforcement steps to keep the sanctions tight."The U.S. referred earlier to South Korea as a partner that is heeding UNSC sanctions, but concerns may develop as new findings continue to surface.A VOA report stated Tuesday that a vessel suspected to have carried coal from North Korea is currently anchored at South Korea's southern port of Pohang, based on data from Marine Traffic.The Belize-flagged vessel Jin Long departed from Russia's Nakhodka Port that handles coal shipments, and is presumed to have entered Pohang carrying coal from Russia, based on satellite images from Planet Labs. It is one of the three vessels Rep. Yoo Ki-june of the main opposition Liberty Korea Party referred to as having brought North Korean coal to the South. The lawmaker leads a taskforce looking into suspicions over North Korean coal imports."The Jin Long, which has been reported as a vessel suspected to have carried North Korean coal, carried 5,100 tons of what is presumed to be coal from Russia's Nakhodka port and entered Pohang port Saturday and will leave today," Yoo said in a press conference Tuesday.The lawmaker as well as data from Marine Traffic state the Jin Long has entered South Korean ports on 18 or 19 occasions since August last year. Resolution 2397 adopted by the UNSC last December states "member states shall seize, inspect and freeze any vessel in their ports" if there are grounds to believe the vessel was involved in activities or the transport of items prohibited by resolutions.The government's stance is that investigations are ongoing, and it is too early to take measures such as seizing suspicious vessels."The government conducted inspections and did not find allegations of UNSC resolution violations," Foreign Ministry spokesman Noh Kyu-duk said in a briefing, Tuesday."Measures such as seizures and inspections must be taken immediately according to the UNSC resolutions for vessels suspected to have carried coal, including the Jing Long," Yoo said.